at limit weights the wing tip is higher than the top of the fuselage.

a lower weight requires a lower lift, therefore the wings are not as loaded as they could be, and therefore a lower aeroelastic reaction.

there are no penalties in having wings that flex, indeed it is a requirement in efficiency for the wings to flex, aeronautically and structurally.

aero elasticity provides a bit of a worry in terms of manouverability, and placement of the wing is important here, (hence why high wing aircraft tend to have some amount of anhedral) this would make the b52 worse off than say a 747 or indeed the a380, but thats not an issue in the cruise.